There are many situations wherein it is important to know both position and orientation of a camera (or eye in an optical see through system). For example, this is the case with an augmented reality system.
Orientation can be determined if all 3 Euler Angles—yaw, pitch and roll—are known. It is relatively straightforward to determine pitch and roll since gravity can be used as a reference and measurements can be made using accelerometers. Yaw, however, is more difficult to determine.
Indeed, even though various references are available including solar or astral sources, Coriolis forces, Earth's magnetic field or introduced infrastructure such as radio beacons to find yaw, for many applications these references are too unreliable, too noisy or require apparatus which is too bulky.
The present technology allows to determine the global azimuth (absolute yaw) without introducing any infra structure to the site (other than that one required for RTK GPS).